Connected: An Internet Encyclopedia
RFC 1072 - 2. TCP WINDOW SCALE OPTION

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### 2. TCP WINDOW SCALE OPTION

The obvious way to implement a window scale factor would be to define a new TCP option that could be included in any segment specifying a window. The receiver would include it in every acknowledgment segment, and the sender would interpret it. Unfortunately, this simple approach would not work. The sender must reliably know the receiver's current scale factor, but a TCP option in an acknowledgement segment will not be delivered reliably (unless the ACK happens to be piggy-backed on data).

However, SYN segments are always sent reliably, suggesting that each side may communicate its window scale factor in an initial TCP option. This approach has a disadvantage: the scale must be established when the connection is opened, and cannot be changed thereafter. However, other alternatives would be much more complicated, and we therefore propose a new initial option called Window Scale.

2.1 Window Scale Option
2.2 Using the Window Scale Option

Next: 2.1 Window Scale Option

Connected: An Internet Encyclopedia
RFC 1072 - 2. TCP WINDOW SCALE OPTION